The envelopment of human cytomegalovirus (HCMV) is complex and requires the incorporation of a large number of viral glycoproteins in the viral envelope surrounding the tegumented particle. Envelope glycoproteins conserved between different herpesviruses, including gB, gH, gL, gM, and gN have been shown to be essential for the production of infectious virions. In contrast to several well studied 1-herpesviruses, both glycoprotein components of the gM/gN complex of HCMV are essential for assembly of infectious virus and interestingly, gM represents the most abundant envelope glycoprotein. Recent findings have indicated that mutations in the cytoplasmic tail of gM that alter its intracellular trafficking to the cytoplasmic assembly compartment (AC) resulted in a replication impaired phenotype of the mutant virus. In addition, mutations in a single amino acid in the cytoplasmic tail of gN resulted in a severely replication impaired virus. In both cases, the phenotype of the mutant viruses was associated with a significant decrease in the assembly of enveloped particles in the infected cell suggesting that either altered trafficking of the gM/gN complex to the AC or altered function of the complex once in the AC resulted in the loss of envelopment of the tegumented particle during this final step in virus assembly. In this application we will explore the role of the gM/gN complex in HCMV envelope assembly by (1) elucidating intrinsic signals in the gM/gN complex required for intracellular trafficking to the AC, (2) defining cellular components of vesicular trafficking required for the localization of gM/gN to the AC, and (3) characterizing viral protein interactions with gM/gN that contribute to the envelopment of the tegumented particle. Our overall goal is to investigate the hypothesis that the gM/gN complex plays a central role in the biogenesis of the HCMV envelope. Findings from these studies could offer new avenues for the development of antiviral agents for the treatment of medically important infections associated with HCMV.